1) Field of the Invention
The present invention relates to an optical scanner and an image forming apparatus, and particularly to an optical scanner and an image forming apparatus that are utilized for optical printer, digital copying machine, plain-paper facsimile, and the like.
2) Description of the Related Art
In an image forming apparatus utilizing an electrophotographic process used in optical printer, digital copying machine, plain-paper facsimile, and the like, the colorization and faster printing have become common, and a tandem type image forming apparatus using a plurality of photoconductors is becoming widespread. In the tandem type image forming apparatus, a larger number of light sources are utilized and consequently the number of components for the apparatus is increased, and this results in a cost increase for the apparatus. In the image forming apparatus, failure of light sources can be cited as the main cause for malfunctions of units that perform optical scanning, and as the number of light sources is increased, a probability of malfunctions becomes higher.
The present inventor has proposed a tandem type image forming apparatus with a reduced number of light sources as disclosed in the Japanese Patent Application Laid-open No. 2002-23085.
In the image forming apparatus described in the patent application, optical scanning paths from one light source toward two photoconductors are formed, the optical scanning paths toward the two photoconductors are sequentially selected with a time lag, and the light beams from one light source are intensity-modulated with image signals corresponding to an optical scanning position optically scanned by the selected optical scanning path, thereby the two photoconductors are optically scanned with light beams from one light source.
Accordingly, since the two photoconductors can be optically scanned with one light source, only two light sources are required even in the tandem type image forming apparatus using four photoconductors.
However, in an embodiment specifically described in the patent application, there is a limitation to speeding-up of image formation because single optical scanning on two photoconductors is performed with the light beams from one light source by one rotation of a optical deflector.